Digital Light Processing (DLP) is a technology used in projectors and video projectors. In DLP applications such as image transmission systems and projectors, a DLP image is created by microscopically small mirrors that are positioned and arranged in a matrix on a semiconductor chip. The “chip” is often referred to as a Digital Micromirror Device (DMD) and is used hereinafter a “chip” or “DMD chip”. Each micromirror, or as used herein “mirror,” on the chip typically represents one pixel in the projected image.
FIG. 1 is a pictorial representation of a mirror 100 in a typical mirror array on a DMD. From FIG. 1, mirror 100 is positioned in proximity to other mirrors 110, 120, 130, 140 and 150 in which there exists a gap between the placement of each mirror at 111, 121, 131, 141, 151, as well as at 161. These gap areas do not reflect light as instead they are required to exist in order to permit the mirrors to angle and reposition during operation. Typically, a support post 170 of each mirror is in contact with a torsion hinge or other mechanical apparatus below the mirror (not shown) to provide the capability of the mirror's movement.
FIG. 2 is a pictorial representation of a larger portion 200 of the mirror array of FIG. 1. A DMD chip typically contains a rectangular array of up to 2 million hinge-mounted mirrors where each of these mirrors is of a dimension less than 20 microns or one-fifth the width of a human hair.
FIG. 3 represents a pictorial representation of the underside of a mirror 300 having a diagonal hinge 310.
FIG. 4 is a cut-away pictorial representation of a mirror on a chip 400. From FIG. 4, mirror 410 is supported by a mirror support post 420, which is balanced on a yoke 430 that is midpoint a hinge assembly 440. As part of the hinge assembly 440, there are two hinge support posts 450 which reside upon metal contact surface 460 above the substrate 470 of the chip 400.
FIG. 5 represents a schematic of a typical DLP system 500. In a typical DLP system a light source 510, a color wheel 520, a chip 530 with associated processor logic (such as but not limited a command logic) 540, and a projection means such as a projection lens 550. From FIG. 5, as the white light source of 510 passes through the color wheel 520, a colored light is reflected from a mirror of the chip 530 in a predetermined manner based on its predetermined mechanical angle position as being ON or OFF, and a resulting colored light is projected through the lens 550 for viewing. In a DLP system, the mirrors on the chip may reflect an all-digital image onto a screen or other projection surface for a viewer's use.
Optically, pixels resulting from the projection, and their associated resolution, are observable by the user's eye. For instance, in FIG. 6, a traditional projection DLP display system is shown 600. From FIG. 6, the system comprises a light source 610, a color wheel 620, a mirror array 630 having, a projection lens 640 and a display screen 650. The light source 610 when emitted after passing though the color wheel 620 is received by a mirror on the array 630. The mirror on the array 630 receiving the colored light is then switched to be ON or OFF in accordance with the desired result, as predetermined, and the resulting color in relation to its angle is displayed on the display screen 650 at that moment. Thereafter, the position of the mirror is again altered and an associated color is then displayed. This process repeats itself thousands of times per second per mirror.
A DLP system will typically vary in the number of mirrors that are present on its respective chip, in view of the resolution sought for a particular system. For instance, the number of mirrors directly affects and corresponds to the resolution of the projected image, such that improved resolution characteristics require a greater number of properly positioned and aligned mirrors on the chip. Typically, resolutions are recognized as 800×600, 1024×768, 1280×720, etc., where resolutions such as 1920×1080 and greater correspond with improved visual sensitivities such as High Definition Television (HDTV). The placement and alignment of the mirrors on the DMD is critical such that the mirrors may be positioned so as to be capable of being repositioned rapidly to reflect light either through the lens, imagery device or a heatsink.
In a DLP system, the mirrors on the chip are often mounted on miniature mechanical hinges or yokes that provide tilting capability to each mirror in relation to the light source of the system and the associated electrodes providing a charge. Typically, the mirrors on the DMD are rapidly repositioned thousands of times per second by one or more electrodes resident therewith from one position to another such that as each mirror changes in angle by upwards of 20 degrees, the light reflected off of the mirror is affected and the resulting reflected light, and its associated intensity, that then passes through a color wheel of the system and eventually to the screen for viewing as a pixel is a direct result of the light reflected.
FIG. 7 is a pictorial representation of a typical mirror 710 underside having two supports (720, 730) and two electrodes (740, 750). Where a voltage source providing current to each electrode acts to decrease voltage applied to one electrode and/or acts to increases a voltage applied to the other electrode, thereby creating an imbalance between the electrostatic attraction generated between each electrode and the mirror, resulting in the mirror to effectively tilt.
In a grayscale image system, where there is no color wheel, reflected light is white, black or a shade of grey, depending on the angle of the mirror. For instance, when a mirror is angled in an “ON” position to reflect light, the resulting light reflected is one of white or a shade of gray. Contradistinctively, when a mirror is angled in an “OFF” position to not reflect light, the result is no light reflected so effectively no light, or black, is passed. Due to the speed of adjustment, visually, when a mirror is switched on more than off, it results in a reflection of a lighter-shade gray pixel, whereas when a mirror is switched on more than off, it results in a reflection of a darker-shade gray pixel. The mirrors are adjusted in relation to commands received from bit-streamed image code of the associated control module resulting in mirrors that may adjust several thousand times per second.
Generally, the movement of the mirrors in a display system includes the use of electrodes, hinges, electrostatic attraction, piezoelectric device, and thermal actuators.
In a color DLP system, the projected white light of the light source, commonly generated by a lamp, typically first traverses through a color wheel positioned prior to the chip. The color wheel filters the projected light into its color scheme, which is often at least red, green, and blue, from which a single-chip DLP projection system is known to create at least 16.7 million colors and a three-chip DLP projection system is known to be capable of producing in excess of 35 trillion colors. Reflected light from the mirrors of the chip is then passed for projection onto a viewing surface where, for example, the color orange (or orange hue) results from a viewer's eye observing red and yellow light simultaneously as a result of rapidly alternating flashes.
As can be appreciated reliable, economical and efficient techniques for having reliable DLP techniques are increasingly of interest particularly given cases where mirrors have become stuck in one position during operation, obvious limits in DLP technology requiring continuous repositioning and precise alignment of mirrors resulting in required gaps between mirror surfaces which do not reflect light, dimensional limitations of mirrors in traditional DLP systems with the resulting inherent limit to improved pixel resolution, and the continuous desire by users to have improved viewing and operational longevity in their projection systems.
Unfortunately, mirrors have become immovable in certain instances, particularly where capillary water condensation has occurred or where van der Waals forces have resulted. Additionally, as a matrix array of mirrors is not continuous for reflectivity of projected light sources, gaps between mirrors also represent projection gaps in a viewer's projected image causing a “screen door” effect which thereby does not result in a projected image that is robust. The screen door effect is also known as fixed-pattern noise (FPN) and is a visual artifact of a plurality of fine lines that separate the projector's pixels, from the gaps between the mirror edges, which become visible in the projected image on the display screen.
Accordingly, what is needed is an apparatus and system for an optically reflective switching device in a display system which though reduces reliance on precise mirror arrangement and angular mechanical performances, improves resulting projected resolution with enhanced operational reliability while being fixedly positioned in a predetermined state.